Neuropeptide Y, Peptide YY, and Sympathetic Control of Rectal Tone and Anal Canal Pressure in the Cat

Sympathetic mechanisms in the regulation of rectal tone and anal canal pressure have been investigated in the cat. Immunohistochemical studies demonstrated neuropeptide Y-like immunoreactivity in noradrenergic cell bodies of the inferior mes-enteric ganglion, in nerve endings in the circular smooth-muscle layers of the rectum and internal anal sphincter, in the myenteric plexuses, and around blood vessels and anal glands. Peptide YY-like immunoreactivity was demonstrated exclusively in endocrine cells of the rectal mucosa. By radioimmunoassay the amount of neuropeptide Y in the inferior mesenteric ganglion was found to be 28.5 (17.8–66.6) pmol g-1, in the rectum 0.8 (0.7–1.6) pmol g-1, and in the anal canal region 0.8 (0.5–1.0) pmolg-1 of tissue. Neuropeptide Y (4–80 pmol kg-1 min-1 intravenously) and peptide YY (1–25 pmol kg-1 min-1 intravenously) increased rectal tone and anal canal pressure. The effects were not inhibited by guanethidine, phentolamine, or propranolol. Noradrenaline (100–1000 pmol kg-l ...